The present invention relates to a method and apparatus for the manufacture of thin film magnetic transducers and, more particularly, to a manufacturing and lapping process for individual magnetoresistive (MR) heads which eliminates the need for electrical lapping guides and provides an MR sensing element having a uniform element height. The present lapping process is particularly applicable to MR heads having relatively long MR sensing elements, such as MR heads for use with magnetic tape systems.
In high speed data processing systems, magnetic recording has been employed for large memory capacity requirements. In magnetic storage systems, data is read from and written on to magnetic recording media utilizing magnetic transducers commonly referred to as magnetic heads. In a magnetic disk drive system, for example, one or more magnetic recording disks are mounted on a spindle such that the disks rotate to permit the magnetic head mounted on a moveable arm in a position closely adjacent the disk surface to read or write information thereon.
During operation, an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disk where the head electromagnetically reads or writes datas. Typically, the magnetic head is integrally mounted in a carrier or support referred to as a "slider". The slider generally serves to mechanically support the head and any electrical connections between the head and the remainder of the disk drive system. The slider is aerodynamically shaped to glide over moving air and therefore to maintain a uniform distance from the surface of the rotating disk thereby preventing the head from undesirably contacting the disk.
In a disk drive system, a slider is typically formed with one surface having two parallel rails separated by a recessed area between the rails and with each rail having a ramp at one end. The surface of each rail that glides over the disk surface during operation is referred to as the air bearing surface. In contrast, in a tape drive system the slider air bearing surface is contoured providing a curved surface facing the magnetic tape media which, as a result of moving magnetic tape wrapped over the air bearing surface at high speed, forms a layer of air which prevents the tape from contacting the slider surface.
The magnetic head may be an inductive electromagnetic device including magnetic pole pieces which read the data from or write data onto the recording media. Alternatively, the magnetic head may include a magnetoresistive read element for separately reading the recorded data, while the inductive head serves only to write the data. In either case, the inductive head magnetic pole pieces and the MR head elements terminate on the air bearing surface and function to electromagnetically interact with the magnetic media.
In the manufacture of such magnetic read/write heads, a large number of sliders and heads are fabricated from a single wafer having rows of the magnetic transducers deposited simultaneously on the wafer surface utilizing semiconductor type process technology. After deposition of the magnetic heads is complete, single row/bars are sliced from the wafer, each bar comprising a row of magnetic head units which can be further processed into sliders having one or more magnetic transducers on their end faces. Sliders having a generally flat air bearing surface designed for use in rotating disk magnetic storage systems may be batch processed wherein a number of the sliders are further processed in rows as sliced from the wafer. Sliders designed primarily for use in magnetic tape storage systems commonly have curved or contoured air bearing surfaces and are required to be processed individually rather than in rows.
In order to achieve optimum efficiency from the magnetic heads, the sensing elements must have a pole tip height dimension commonly referred to as throat height for the thin film inductive heads, or element height in the case of the MR read heads, which must be maintained within a certain limited tolerance for generating an optimum signal from a given head element. During the slider processing, it is critical to grind or lap the slider to a desired thickness in order to achieve the desired throat height and MR element height for the magnetic head.
A method of producing a required element height includes a lapping stage in which an abrasive grinding surface accurately grinds the inductive pole tips and MR elements to a desired length (i.e., height). Suitable techniques for controlling the MR element height during the lapping operation include measuring the resistance of the MR element as it is lapped to the final element height. The change in resistance of the MR element at any given time during the lapping operation indicates the amount of the material that has been removed from the elements. Since the resistance of the MR element is proportional to the amount of MR material remaining, the resistance is an indication of the final element height of the MR element being lapped.
As discussed above, in an MR head oftentimes the MR element is used as the lapping guide to control the final height of the MR element. The resistance of the MR element is used to determine when the desired element height has been achieved. During the lapping process, the plane of the lapped surface can become skewed with respect to the MR element, resulting in one end of the MR element being higher than required and the other end being lower than required when the MR element is exhibiting the target resistance. This problem is not significant when lapping an array tape head or a row of sliders because multiple elements are being monitored. For example, U.S. Pat. No. 4,914,868, assigned to the instant assignee, discloses an apparatus and process for eliminating curvature, referred to as bow, in a row of magnetic transducers during lapping. As shown in FIG. 1, electronic lapping guides (ELG) are provided at each end of the row of magnetic transducers. A lapping skew is indicated when there is significant differences in the measured resistance of the ELGs located at the extreme ends of the row.
For magnetic heads which are lapped individually skew control is critical, particularly for some magnetic tape head designs wherein the MR element is long relative to its height. U.S. Pat. No. 4,155,106 issued May 15, 1979 discloses a magnetic head including plural leads for use during the manufacturing process to monitor the progress of the lapping operation. As shown in FIG. 4, the outer leads 14a on either side on the head are utilized with detector leads 15 and 16 to monitor the progress of the grinding operation. The described magnetic head requires that additional leads 14a be provided during manufacture of the head thus increasing the physical size of the head and reducing the number of heads that may be fabricated on a given wafer.